1. Field of the Invention
The present invention relates to a method of preparing a polymer containing functional groups by reacting a polymer containing alkenyl groups with a silicon polyhydride compound.
2. Description of the Related Art
Conventionally, the molecular weight of a polymer containing functional groups obtained by a transformation of functional group is determined by the molecular weight of the polymer used as its raw material. Since the molecular weight between chemical crosslinks is equal to the molecular weight of the starting polymer. Therefore, in the case where a polymer containing functional groups is made to serve as a curable composition utilizing its functional group, the properties of the product polymer obtained are inevitably restricted according to the molecular weight of starting material.
For example, for preparation of a polymer containing a plurality of alkenyl groups in one molecule from a polyisobutylene serving as a starting polymer, methods disclosed in U.S. Pat. No. 4,316,973, Jap. Pat. Appln. KOKAI Publications Nos. 63-105005 and 4-103606 and the like, can be considered. However, in any of these methods, a polyisobutylene is prepared by the cationic polymerizing method for isobutylene monomers in a solvent (inifer method). However, when the molecular weight of the polymer obtained by the polymerization is excessively high, polymer is precipitated out from the polymerization system, thus resulting in an ununiformal reaction. Therefore, in practice, the molecular weight can only be achieved up to 5,000 to 10,000 at most.
In the meantime, for preparation of a polymer containing a plurality of silyl groups in one molecule, methods disclosed in Jap. Pat. Appln. KOKAI Publications Nos. 63-006003 and 1-197509 and the like, can be considered. However, the starting polymer is a polymer containing alkenyl groups in each of the these publications, and therefore it is difficult to prepare an oligomer having a molecular weight of higher than 10,000 for the same reason as indicated above. Even if an oligomer having a molecular weight of 10,000 or more is prepared, the molecular-weight distribution will be broader due to the ununiformity of the reaction, which is caused by the precipitation of the polymer, which is caused by the separating of oligomer, and the introduction of functional groups such as alkenyl groups cannot be completely performed.
Further, if the molecular weight exceeds 10,000, the viscosity of the obtained oligomer increases remarkably. As a result, the pumping out and transfer of a product, which follows the completion of the purification and concentration step after polymerization, cannot be performed or easily carried out, creating a problem of a low workability.
In the case where such a polymer is used as a curable composition, the usage of the product is limited because of the lack of elongation. This lack of extensibility is caused by the fact that the molecular weight between chemical crosslinks after curing is low when the molecular weight is 10,000 or less.